1. Field of the Invention
The invention relates to the configuration, fitting and operation of a mask suitable for the delivery of non-invasive positive pressure ventilation and for nasal CPAP treatment of sleep disordered breathing conditions such as obstructive sleep apnea.
2. Description of Related Art
Obstructive Sleep Apnea (OSA) is a disease characterized by excessive daytime sleepiness, loud snoring and daytime irritability. Other effects of OSA can include depression, high blood pressure, serious heart conditions, sexual problems, memory lapses, intellectual deterioration and morning headaches. The treatment of OSA by the application of nasal Continuous Positive Air Pressure (CPAP) was invented by Sullivan and is described in U.S. Pat. No. 4,944,310 (Sullivan, assignee ResMed Limited). The technique involves the application of a flow of pressurized breathable gas (typically room air) to either the nose or nose and mouth of a patient while they sleep. This technique is said to “splint” open the airways. Typical treatment pressures are in the range of 3 to 20 cm H2O. Flows are up to approximately 200 L/min. Usually the flow of pressurized air is produced by a blower and delivered to the patient via a patient interface. The source of the air flow and patient interface are joined by a conduit. Whilst there are other techniques for the treatment of OSA such as surgery, the use of CPAP has become the “gold” standard. For a particular patient the pressure which is needed to maintain open airways can vary throughout the night and vary on different nights. U.S. Pat. No. 5,245,995 (Sullivan and Lynch, assignee ResMed Limited) describes a method and device for varying the pressure in accordance with indications. For example, if the patient starts to snore, the pressure automatically increases, whilst in the absence of snoring the pressure automatically decreases.
Non-Invasive Positive Pressure Ventilation (NIPPV) is another form of treatment for breathing disorders. In its most basic form it involves a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. Typical treatment pressures are in the range of 3 to 30 cm H2O.
In other NIPPV modes the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment, as disclosed in international PCT patent applications PCT/AU97/00631 (Berthon-Jones, assignee ResMed Limited) and PCT/AU99/00386 (Berthon-Jones, assignee ResMed Limited).
In this specification, any reference to CPAP treatment is to be understood as embracing all of the above-described forms of ventilatory treatment or assistance.
One of the earliest patient interfaces for providing CPAP treatment was constructed to include a fiberglass model of the patient's nose. The model was adhered to the patient's nose each night and removed each morning An advantage of this patient interface included the customized fit which assisted in achieving a good seal between the patient interface and the patient's airways. However the use of adhesive to secure the mask was inconvenient and not desirable.
Another suitable patient interface is described in U.S. Pat. No. 5,243,971 (Sullivan and Bruderer, assignee University of Sydney) entitled “Nasal Mask for CPAP having Ballooning/Moulding Seal with Wearer's Nose and Facial Contours”.
This patent describes a nasal mask with a soft face-contacting portion and a rigid shell. The mask is held in position using headgear. The headgear is attached to the mask shell and passes around the back of the wearer's head. The patent depicts two sets of straps in the headgear. The first set comprised a pair of straps passing from the forehead region to the back of the head. The second set comprised a pair of straps passing from the nasal region of the mask to the back of the head.
Another known patient interface is the MIRAGE® nasal mask (by ResMed Limited). This nasal mask includes a pair of headgear attachment points in the nasal region of the mask shell and a forehead support which includes another pair of headgear attachment points. The forehead support to this mask is the subject of U.S. Pat. No. 6,119,693 (Kwok, Matchett & Grant, assignee ResMed Limited). The headgear comprises a single piece of a soft, flexible composite fabric with a generally triangular back portion and four straps. The four straps comprise a pair of upper straps and a pair of lower straps connecting to the headgear attachment points on the forehead support and nasal mask shell respectively. At the end of each strap is secured a piece of hook and loop fastening material such as Velcro™ which, in use, passes through a headgear attachment point and fastens on corresponding loop material on the strap. The generally triangular back portion engages the skull in the region of the occiput. The fabric stretches under a load. The base of the triangle is positioned near and generally in line with the upper straps.
Some patients open their mouths during sleep which means that they may not receive the benefit of nasal CPAP due to mouth leaks. Various solutions have been proposed for this problem. One solution is taught in U.S. Pat. No. 6,123,082 (Berthon- Jones, assignee ResMed Limited), whereby the lips are held closed. Another solution is to use a mask which covers both the nose and mouth of the patient. An example of a mouth and nasal mask is described in U.S. Pat. No. 5,560,354 (Berthon-Jones, Calluaud, Lynch & Hely, assignee ResMed Limited).
Another suitable mask system is the MIRAGE® full face mask (by assignee ResMed Limited). The MIRAGE® full face mask and headgear is illustrated in FIG. 1. Suitable headgear for this mask is constructed from a composite material of nylon, neoprene and hook and loop material. The headgear similarly comprises a pair of upper and a pair of lower straps and a generally triangular back portion. The upper strap has a total length of approximately 610 mm. The straps have an approximate width of 25 mm, however the upper strap has an approximate width of 19 mm. The triangular region has a base of approximately 15.5 cm and two equal sides of approximately 11 cm. The upper and lower straps are approximately 192 mm apart. In addition, the headgear includes a quick release mechanism as described by U.S. Pat. No. 6,422,238 (Lithgow, assignee ResMed Limited). The quick release mechanism provides a “rip cord” which can be pulled upon to separate the headgear and hence remove the mask in an emergency. When the headgear is positioned on the patient's head, the quick-release mechanism is situated at the back of the head and the cord runs through loops towards the front of the mask system.
Patient interface arrangements include nasal masks, nose and mouth masks, nasal prongs and nasal pillows. In all forms of patient interface used with CPAP for treating sleep disordered breathing, there is a need to counterbalance the force of the pressurized air and to correctly position the interface. Since the patient must sleep with this interface, it is important that it be comfortable. From the manufacturing and distribution channel perspectives, it is advantageous if one size of headgear fits a large range of head shapes and sizes.
Other examples of prior art headgear and mask shells have configurations which are different to those depicted in U.S. Pat. No. 5,243,971 and used in the MIRAGE® nasal mask and MIRAGE® full-face mask in so far as they incorporate a different number of headgear straps or differ in the placement of the head strap attachment points or both. This variety of mask configurations is required to address the biological variability existing between users, each user having a unique facial and. head shape. However no one mask system involving headgear and fixed point strap attachment points offers continuous variability in placement. As a result, when selecting from a range of mass produced mask and headgear systems, in the majority of cases the selection will represent a compromise for the user where a balance must be struck between comfort and the achievement of a secure fit and good seal between the mask and the user.
An approach to headgear attachment which allows for great variability in head strap number and attachment position to the mask would yield great benefits to the user in terms of comfort and function, to the mask system manufacturer in terms of facilitating the opportunity to easily experiment with different mask positions and headgear configurations while moving towards the desirable objective of rationalising manufacturer and supplier inventory.
It should be noted that while there are many mask and headgear arrangements available for ventilators, respirators, aviator masks and other breathing apparatus, generally these may not be suitable for use in the treatment of sleep disordered breathing because they are not sufficiently comfortable to allow the patient to sleep.
The present invention is directed towards providing a method of configuring a mask and a mask for use in the treatment of sleep disordered breathing which improves patient comfort, is long lasting and fits a wide range of head shapes and sizes.